Pharmacokinetics of ketorolac in wild Eastern box turtles (Terrapene carolina carolina) after single intramuscular administration.

Ketorolac is a nonsteroidal anti-inflammatory drug that possesses potent analgesic activity comparable to morphine. The opioid shortage in the United States has led to an unreliable supply of opioids for use in rehabilitation facilities, thus underscoring the need for research on the safe and effective use of nonopioid alternatives. The goal of this study was to determine the pharmacokinetics of ketorolac after a single 0.25 mg/kg intramuscular injection administered to injured Eastern box turtles (Terrapene carolina carolina). A sparse blood sampling protocol was used to collect samples from 32 wild turtles that presented to the Turtle Rescue Team at North Carolina State University for traumatic injuries. Blood was collected from 0 to 24 hr after injection and analyzed via high-pressure liquid chromatography (HPLC). A nonlinear mixed-effects (NLME) model was fitted to the data to obtain typical values for population parameters. Using this approach, we identified a long half-life (T1/2 ) of 9.78 hr and a volume of distribution (Vss ) of 0.26 L/kg. We have concluded that this long T1/2 for a dose of 0.25 mg/kg ketorolac-injected IM provides plasma levels above a previously published target level for 24-hour analgesia to allow for once daily dosing.

Enantiomer-specific ketorolac pharmacokinetics in young women, including pregnancy and postpartum period.

Racemic ketorolac clearance (CL) is significantly higher at delivery, but S-ketorolac disposition determines the analgesic effects. The aim of this study was to investigate the effect of pregnancy and postpartum period on enantiomer-specific (S and R) intravenous (IV) ketorolac pharmacokinetics (PKs). Data in women shortly following cesarean delivery (n=39) were pooled with data in a subgroup of these women that was reevaluated in the later postpartum period (postpartum group, n=8/39) and with eight healthy female volunteers. All women received single IV bolus of 30 mg ketorolac tromethamine. Five plasma samples were collected at 1, 2, 4, 6, and 8 hours and plasma concentrations were determined using high performance liquid chromatography. Enantiomer-specific PKs were calculated using PKSolver. Unpaired analysis showed that distribution volume at steady state (Vss, L/kg) for S- and R-ketorolac was significantly higher in women shortly following cesarean delivery (n=31) compared to postpartum group (n=8) or to healthy female volunteers (n=8). CL, CL to body weight, and CL to body surface area (CL/BSA) for S- and R-ketorolac were also significantly higher in women following delivery. In addition, S/R-ketorolac CL/BSA ratio was significantly higher at delivery. Paired PK analysis in eight women shortly following delivery and in postpartum group showed the same pattern. Finally, the simultaneous increase in CL and Vss resulted in similar estimates for elimination half-life in both unpaired and paired analysis. In conclusion, pregnancy affects S-, R-, and S/R-ketorolac disposition. This is of clinical relevance since S-ketorolac (analgesia) CL is even more increased compared to R-ketorolac CL, and S/R-ketorolac CL ratio is higher following delivery compared to postpartum period or to healthy female volunteers.

Analytical and semi-preparative enantioresolution of (RS)-ketorolac from pharmaceutical formulation and in human plasma by HPLC.

An efficient, simple, validated, analytical and semi-preparative HPLC method has been developed for direct enantioresolution of (RS)-Ketorolac (Ket) using monochloro-methylated derivatives of cellulose and amylose, i.e. cellulose (tris-3-chloro-4-methylphenylcarbamate) and amylose (tris-5-chloro-2-methylphenylcarbamate) as chiral stationary phases (CSPs) with photo diode array detection at 320 nm. Enantioresolution was carried out in samples of human plasma spiked with (RS)-Ket under normal and reversed-phase elution modes with suitable mobile phase compositions. The effect of nature of alcohols (MeOH, EtOH, PrOH and n-BuOH) and other solvents (MeCN and MeOH) as organic modifiers in the mobile phase was investigated on the separation performance of two CSPs in terms of retention and separation of enantiomers. The best resolution was observed on cellulose-based CSP using EtOH, while using 2-PrOH (15%) and amylose-based CSP obtained the highest retention. Under reversed-phase elution mode the best enantioseparation was observed using 30% MeCN with ammonium formate buffer. The elution order of enantiomers was ascertained by determining specific rotations. The limit of detection and quantitation values were 5 and 15.5 ng/mL for each enantiomer of (RS)-Ket, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Pharmacokinetics of intravenous ketorolac in cats undergoing gonadectomy.

AIM: To determine the pharmacokinetics of ketorolac tromethamine (0.5 mg/kg) when administered I/V to cats undergoing gonadectomy. METHODS: Ketorolac was administered to nine female and three male shorthair domestic cats as an I/V bolus of 0.5 mg/kg after intubation, and 20 minutes prior to ovariectomy or orchiectomy. Intra-operative cardiorespiratory variables were monitored and blood samples were collected over 24 hours. Concentrations of ketorolac in serum were determined by high-performance liquid chromatography to establish pharmacokinetic parameters. RESULTS: During surgery, mean end tidal isoflurane concentration was 1.63 (SD 0.24)% and normocapnia and spontaneous ventilation were maintained in all animals. The kinetics of ketorolac was described by a two-compartment model. The distribution and elimination half-lives were 0.09 (SD 0.06) and 4.14 (SD 1.18) hours, respectively. The body clearance was 56.8 (SD 33.1) mL/h/kg. The volume of distribution at steady-state and the mean residence time were 323.9 (SD 115.7) mL/kg and 6.47 (SD 2.86) hours, respectively. CONCLUSION AND CLINICAL RELEVANCE: On the basis of the results, concentrations of ketorolac in serum in cats were above the human effective concentrations for 5-6 hours postoperatively. However, other studies including a control group are advocated to further investigate the ketorolac kinetics and the analgesic efficacy in this species.

Plasma concentration of ketorolac after local infiltration analgesia in hip arthroplasty.

BACKGROUND: Local infiltration analgesia (LIA) with local anaesthetic (ropivacaine), a nonsteroidal anti-inflammatory drug (ketorolac) and epinephrine after lower extremity arthroplasty has gained increasing popularity during the last decade. This method has certain advantages, which include minimal systemic side effects, faster post-operative mobilization, earlier post-operative discharge from hospital and less opioid consumption. However, information regarding plasma concentrations of ketorolac after LIA mixture is insufficient to predict the risk of renal impairment in patients subjected to arthroplasty. AIM: To determine the maximal plasma concentration and the exposure of ketorolac during the first 30 h following LIA in hip arthroplasty. METHODS: Thirteen patients scheduled for primary total hip arthroplasty with LIA (ropivacaine 200 mg, ketorolac 30 mg and epinephrine 0.5 mg in a volume of 106 ml) were included. Plasma concentration of ketorolac was quantified by liquid chromatography-mass spectrometry. In addition, we assessed the effect of increasing age and decreasing glomerular filtration rate on the maximal plasma concentration and the total exposure to ketorolac during 30 h. RESULTS: The range of the maximal plasma concentration, 0.3-2.2 mg/l, was detected 30 min-4 h after completing the infiltration. Similar plasma levels have been reported after intramuscular injection of the same dose of ketorolac to healthy elderly volunteers. CONCLUSION: Exposure to ketorolac after LIA may be comparable to an intramuscular injection of the same dose. Decision of dose reduction should be based on clinical assessment of risk factors.

Novel stereoselective high-performance liquid chromatographic method for simultaneous determination of guaifenesin and ketorolac enantiomers in human plasma.

A novel method was developed for the simultaneous determination of guaifenesin (GUA) and ketorolac tromethamine (KET) enantiomers in plasma samples. Since GUA probably increases the absorption of coadministered drugs (e.g., KET), it would be extremely important to monitor KET plasma levels for the purpose of dose adjustment with a subsequent decrease in the side effects. Enantiomeric resolution was achieved on a polysaccharide-based chiral stationary phase, amylose-2, as a chiral selector under the normal phase (NP) mode and using ornidazole (ORN) as internal standard. This innovative method has the advantage of the ease and reliability of sample preparation for plasma samples. Sample clean-up was based on simply using methanol for protein precipitation followed by direct extraction of drug residues using ethanol. Both GUA and KET enantiomers were separated using an isocratic mobile phase composed of hexane/isopropanol/trifluoroacetic acid, 85:15:0.05 v/v/v. Peak area ratios were linear over the range 0.05-20 µg/mL for the four enantiomers S (+) GUA, R (-) GUA, R (+) KET, and S (-) KET. The method was fully validated according to the International Conference on Harmonization (ICH) guidelines in terms of system suitability, specificity, accuracy, precision, robustness, and solution stability. Finally, this procedure was innovative to apply the rationale of developing a chiral high-performance liquid chromatography (HPLC) procedure for the simultaneous quantitative analysis of drug isomers in clinical samples.

Development of an enantiomer selective microsampling assay for the quantification of ketorolac suitable for paediatric pharmacokinetic studies.

BACKGROUND: Ketorolac, a potent nonsteroidal anti-inflammatory drug used for pain control in children, exists as a racemate of inactive R (+) and active S (-) enantiomers. AIM: To develop a microsampling assay for the enantioselective analysis of ketorolac in children. METHODS: Ketorolac enantiomers were extracted from 50 µl of plasma by liquid­liquid extraction and separated on a ChiralPak AD-RH. Detection was by a TSQ quantum triple quadrupole mass spectrometer with an electrospray ionisation source operating in a positive ion mode. Five children (age 13.8 (1.6) years, weight 52.7 (7.2) kg), were administered intravenous ketorolac 0.5mg/kg (maximum 10mg) and blood samples were taken at 0, 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h post administration. CL, VD and t1/2 were calculated based on non-compartmental methods. RESULTS: The standard curves for R (+) and S (-) ketorolac were linear in the range 0­2000 ng/ml. The LLOQs of the method were 0.15 ng on column and 0.31 ng on column for R (+) and S (-) ketorolac, respectively. The median (range) VD and CL of R (+) and S (-) ketorolac were 0.12 l/kg (0.07­0.17), 0.017 l/h/kg (0.12­0.29) and 0.17 (0.09­0.31) l/kg, 0.049 (0.02­0.1) l/h/kg, p = 0.043), respectively. The median (range) elimination half-life (t1/2) of the R (+) and S (-) ketorolac was 5.0 h (2.5­5.8) and 3.1 h (1.8­4.4), p = 0.043), respectively. CONCLUSION: The development of a simple, rapid and reliable ketorolac assay suitable for paediatric PK studies is reported.

Mass spectrometric QUAL/QUAN approaches for drug metabolism and metabolomics.

A liquid chromatography-high-resolution mass spectrometry platform was used for simultaneous qualitative and quantitative (QUAL/QUAN) acquisition, enabling drug metabolism and metabolomics investi- gations. Plasma study samples were monitored for three different groups of patients at a single time-point (1 h after drug administration): one group received acetaminophen (APAP), one group received both APAP and ketorolac and one group was a control group. The quantification of APAP and two of its metabolites (APAP-glucuronide and APAP-cysteine) was performed on a fast acquisition quadrupole-Time-Of-Flight (50-100 ms duty cycle, resolving power of 30,000) compatible with UHPLC time constraints. High-resolution Selected Reaction Monitoring was used for quantification of APAP and its metabolites from 50-10,000 ng/mL using a 50 µL plasma aliquot. Average measured concentrations were for APAP 6,650 ng/mL vs 6,160 ng/mL, APAP-CYS concentrations were 154.2 ng/mL vs 140.6 ng/mL and APAP-GLU concentrations 8,750 ng/mL vs 8,430 ng/mL between the group that received only APAP (n = 11) and the group that received APAP in combination with ketorolac (n = 11). No major differences were observed between the two groups of patients, as it would be expected due to the differing metabolism pathway for both substances. For the qualitative aspect, a metabolomics data processing platform with biological QC samples was applied to the study samples to search for unanticipated metabolites and biomarkers related to APAP and ketorolac metabolism. Multivariate analysis (i.e. Principle Component Analysis), variables grouping tools (i.e. PCVG) and high-resolution MS(/MS) spectra from the MS(ALL) acquisition strategy enabled the profiling and characterization of circulating metabolites of APAP in plasma such as APAP-sulfate, APAP-mercapturate as well as ketorolac.

[Influence of Perftoran nanoemulsion on blood plasma concentrations of lipophilic drugs].

The influence of perfluorocarbon blood substitute Perfloran on the plasma concentrations of bendazole, drotaverine, ketorolac and verapamil upon intravenous introduction after Perfloran infusion (5 ml/kg) has been investigated on rabbits. It has been found that the plasma concentrations of verapamil, drotaverine and bendazole (highly lipophilic drugs with log(P) = 4.5, 4.9 and 3.5, respectively) increased in the presence of Perfloran. The influence of Perfloran on the concentration of weakly lipophilic ketorolac was less significant. Perfloran effectively bound drotaverine, ketorolac and verapamil in vitro, whereas the binding of ketorolac by the emulsion particles was weak. Evidently, the infusion of hydrophobic nanoemulsion Perftoran elevates the sorption capacity of plasma and creates prerequisites for the redistribution drugs and favors increase in their concentrations.

Development and validation of liquid chromatography-mass spectrometric method for simultaneous determination of moxifloxacin and ketorolac in rat plasma: application to pharmacokinetic study.

A highly sensitive, selective and rapid liquid chromatography-electrospray ionization mass spectrometry (LC-MS) method has been developed and validated for simultaneous determination of moxifloxacin (MFX) and ketorolac (KTC) in rat plasma. Gemifloxacin (GFX) was used as an internal standard (IS). A simple protein precipitation method was used for the extraction of analytes from rat plasma. Effective chromatographic separation of MFX, KTC and GFX was achieved on a Kromasil C(18) column (100 × 4.6 mm, 5 µm) using a mobile phase consisting of acetonitrile-10 mm ammonium acetate (pH 2.5)-0.1% formic acid (50:25:25) in an isocratic elution, followed by detection with positive ion electrospray ionization mass spectrometry using target ions of [M + H](+) at m/z 402 for MFX, m/z 256 for KTC and m/z 390 for GFX in selective ion recording mode. The method was validated over the calibration range of 5-100 ng/mL for MFX and 10-6000 ng/mL for KTC. The method demonstrated good performances in terms of intra- and inter-day precision (0.97-5.33%) and accuracy (93.91-101.58%) for both MFX and KTC, including lower and upper limits of quantification. The recoveries from spiked control samples were >75% for MFX and >79% for KTC. The matrix effect was found to be negligible and the stability data were within acceptable limits. Further, the method was also successfully applied to a single-dose pharmacokinetic study in rats. This method can be extended to measure plasma concentrations of both drugs in human to understand drug interaction and adverse effects.

[The application of chromatography and spectrometry for the analysis of ketorolac and diclofenac in biological fluids].

The objective of the present work was to study conditions for isolation of ketorolac and diclofenac from biological fluids. A method of their extraction with a mixture of organic solvents has been developed and the conditions for the identification of these compounds are proposed with the use of high performance liquid chromatography (HPLC), UV spectroscopy, and gas chromatography with electron capture detection (GC/ECD). The possibilities of using HPLC, UV spectrometry, and GC/ECD for quantitative determination of ketorolac and diclofenac are illustrated.

An in vivo porcine evaluation of the safety, bioavailability, and tissue penetration of a ketorolac drug-eluting ureteral stent designed to improve comfort.

BACKGROUND AND PURPOSE: Ureteral stents often cause significant patient morbidity that can be difficult to treat. Drug-eluting stent technology allows the local delivery of a drug. Our previous work demonstrated that ketorolac instilled intravesically at the time of ureteral stent insertion significantly decreased flank pain compared with controls. We sought to determine the safety of a novel ketorolac-eluting ureteral stent. MATERIALS AND METHODS: A total of 92 Yorkshire pigs were randomized to 1 of 5 groups. The oral control group consisted of 12 animals with transurethrally inserted control ureteral stents and 5 days of oral ketorolac. Twenty animals in each of the remaining groups received a control stent, or 15%, 13%, or 7% ketorolac-loaded stents. Ketorolac levels were measured in plasma, urine, and tissue sampled from ureters, bladder, kidneys, and liver using high performance liquid chromatography. Necropsies were performed to evaluate tissue pathology. RESULTS: The majority of ketorolac was released within the first 30 days. The highest levels of ketorolac in plasma, kidney, and liver occurred in the oral control group. The highest levels of ketorolac found in ureteral and bladder tissues occurred in the ketorolac-stent groups in a dose-dependent fashion. No adverse events were noted in any of the ketorolac-stent groups. Gastric ulcerations were identified only in the oral control group. No abnormalities were identified in any other internal organs in any group. CONCLUSIONS: The use of ketorolac-eluting ureteral stents has proven to be safe in a porcine model. The ketorolac-stent group had less than 12% of the ketorolac concentration in plasma, kidney, and liver tissues compared with the oral ketorolac group. Ureteral tissues displayed the highest levels of ketorolac. Clinical studies are needed to determine if ketorolac-elution reduces stent symptoms.

[Thin layer chromatography for the analysis of certain anti-inflammatory medicines].

This work was devoted to the elucidation of conditions for isolation of ketorolac and diclofenac from biological fluids. A method is proposed for the extraction of these compounds from solutions with organic solvents at different pH values. Other methods permit to optimize identification of analytes by thin layer chromatography while the densitometric technique may be used for qualitative and quantitative analysis of their composition in biological fluids.

Two-dimensional liquid chromatography-ion trap mass spectrometry for the simultaneous determination of ketorolac enantiomers and paracetamol in human plasma: application to a pharmacokinetic study.

A bioanalytical method was developed for the simultaneous determination of paracetamol and ketorolac enantiomers in human plasma using two-dimensional liquid chromatography-mass spectrometry. Separation was first achieved in a reversed-phase C18 column by using a gradient solvent system consisting of 0.1% aqueous formic acid and acetonitrile (ACN). The effluent between 8.9 and 9.9 min, corresponding to phenacetin and racemic ketorolac peaks, was transferred to a polysaccharide-based chiral column (ChiralPak AD-RH) by using a six-port switching valve. Ketorolac enantiomers were subsequently separated on the chiral column using an isocratic mobile phase composed of ACN/0.1% formic acid 50:50 (v/v). The total run-time was less than 18 min. This innovative strategy prolongs the lifetime of chiral columns by avoiding damages due to the sample matrix. The detection was carried out with an ion trap mass spectrometer equipped with an electrospray ionisation source. The tested ranges were 0.05-20 microg/ml for paracetamol and 0.005-2 microg/ml for each ketorolac enantiomer. This method was fully validated and showed good performances in terms of trueness (80-110%) and precision (6.7-13.2%). The mean extraction recoveries were 60%, 72% and 76% for paracetamol, R-ketorolac and S-ketorolac, respectively. Finally, this procedure was successfully applied to a pharmacokinetic study.

Enantiomeric disposition of ketorolac in goats following administration of a single intravenous and oral dose.

The purpose of this study was to investigate the stereospecific pharmacokinetics of ketorolac (KT) in goats following a single 2 mg/kg intravenous (i.v.) dose and a single 6 mg/kg oral dose. A stereoselective high pressure liquid chromatography assay was used to quantify ketorolac plasma concentrations. Pharmacokinetic parameters for both stereoisomers were estimated by model independent methods. Following an i.v. dose, the plasma concentration profiles for the stereoisomers were similar with half-lives of 1.05 +/- 0.62 h for R-KT and 1.05 +/- 0.61 h for S-KT. Clearance values for R- and S-KT after an i.v. dose were 0.53 +/- 0.23 and 0.54 +/- 0.23 L.h/kg, respectively. Following an oral dose, the terminal half-lives were longer with values of 34.08 +/- 11.81 and 33.97 +/- 12.19 h for R-KT and S-KT, respectively. The average bioavailability was 133 +/- 23% for R-KT and S-KT, respectively. The longer half-lives and high apparent bioavailability after oral dosing are suggestive of a slow absorption process in the gastrointestinal tract and recycling. The results indicate that interconversion of the stereoisomers of ketorolac is absent in goats. However, studies with individual isomers are needed before any conclusion can be drawn about the lack of bioinversion.

How readily does ketorolac penetrate cerebrospinal fluid in children?

Ketorolac is a potent nonsteroidal anti-inflammatory analgesic used in postoperative pain management. Ketorolac elicits its analgesic action by inhibiting the cyclo-oxygenase enzyme in peripheral tissues and in the spinal cord. Central nervous system penetration of parenteral ketorolac has been evaluated in adults but not in children. In the present study we investigated ketorolac cerebrospinal fluid penetration via spinal anesthesia in 30 healthy children undergoing surgery in the lower part of the body. A single cerebrospinal fluid and blood sample was obtained between 11 minutes and 6 hours after receiving ketorolac 0.5 mg x kg(-1) IV. Ketorolac concentrations were determined by gas chromatography with mass spectrometric detection. Ketorolac was detected from 22 of the 30 cerebrospinal fluid samples, and the concentrations ranged between 0.2 and 7.6 microg x L(-1) (median, 0.6 microg x L(-1)). The cerebrospinal fluid to unbound plasma concentration-ratio ranged between 0.01 and 0.69 (median, 0.08). These low concentrations indicate that ketorolac does not readily penetrate cerebrospinal fluid in children.

Synthesis, characterization and pharmacological evaluation of amide prodrugs of ketorolac.

Ketorolac (KC) suffers from the general side effects of NSAIDs, owing to presence of free carboxylic acid group. The study aimed to retard the adverse effects of gastrointestinal origin. Ten prodrugs of KC were synthesized by amidation with ethyl esters of amino acids, namely, glycine, l-phenylalanine, l-tryptophan, l-valine, l-isoleucine, l-alanine, l-leucine, l-glutamic acid, l-aspartic acid and beta-alanine. Purified synthesized prodrugs were characterized by m.p., TLC, solubility, partition coefficients, elemental analyses, UV, FTIR, NMR and MS. Synthesized prodrugs were subjected for biopharmaceutical studies, analgesic, anti-inflammatory activities and ulcerogenic index. Marked reduction of ulcerogenic index and comparable analgesic, anti-inflammatory activities were obtained in all cases as compared to KC. Among synthesized prodrugs, viz. AR-11, AR-19 and AR-20 showed excellent pharmacological response and encouraging hydrolysis rate both in SIF and in 80% human plasma. Prodrugs with increased aliphatic side chain length or introduction of aromatic substituent showed enhanced partition coefficient but diminished dissolution and hydrolysis rates. Such prodrugs can be considered for sustained release purpose.

An effective dose of valdecoxib in experimental mouse models of pain.

The effects of selective cyclooxygenase-2 (COX-2) inhibitors in biological functions are frequently investigated in animal models. However, there is little data on their analgesic efficacy in experimental animals. This study aimed to determine whether oral gavage of 5 mg/kg valdecoxib in mice is active as an analgesic at this dose and whether it is associated with therapeutic blood levels. A nonselective COX inhibitor, ketorolac, was also investigated for comparison. A total of 106 C57 BL/6N mice were administered a single oral dose of 5 mg/kg of valdecoxib, ketorolac or placebo. The antinociceptive effects of both drugs were tested using hot-plate and formalin tests. For the hot-plate test, reaction time (latency) of the mouse before jumping was recorded. The total time that the mouse spent on licking/biting the injected paw (with dilute formalin) was recorded in the formalin test. Apart from the behavioral tests, plasma concentrations of the drugs at this dose were also determined. Mice were fed with 5 mg/kg of either valdecoxib or ketorolac. Blood samples were collected between 1 and 9 h postingestion. Valdecoxib and ketorolac concentration in the plasma was determined by high performance liquid chromatography with ultraviolet detection (HPLC-UV). Effective antinociception was observed for both drugs in the hot-plate test from 75 min to 2 h after oral dosing. Also, both drug treatments showed a significantly reduced nociceptive response in the second phase in the formalin test (20-30 min after injection). Both valdecoxib and ketorolac showed plasma concentrations comparable to the therapeutic concentrations in humans. A single oral dose of valdecoxib or ketorolac (5 mg/kg) is able to produce a therapeutic analgesic effect in mice.

Stereoselective pharmacokinetics of ketorolac in calves after a single intravenous and oral dose.

The purpose of this study was to establish the stereospecific pharmacokinetics of ketorolac (KT) in calves following a single 2 mg/kg intravenous (i.v.) and a single 8 mg/kg oral dose. Plasma concentrations were determined using a stereoselective HPLC assay. Pharmacokinetic parameters for both the stereoisomers were estimated by model-independent methods. Following an i.v. dose, the plasma concentration profiles of the stereoisomers were similar with half-lives of 5.9 +/- 5.1 h for R-KT and 6.0 +/- 4.9 h for S-KT. Clearance values for R- and S-KT after an i.v. dose were 0.0470 +/- 0.0370 and 0.0480 +/- 0.0370 L/h/kg respectively. After an oral dose, the terminal half-lives were longer than following i.v. administration with values of 14.77 +/- 3.08 and 14.55 +/- 2.95 h for R-KT and S-KT respectively. The average oral bioavailability was 86.5 +/- 20.6% for R-KT and 86.7 +/- 20.3% for S-KT. The results indicate that the stereoisomers of KT have similar pharmacokinetic profiles in calves. Although, unlike humans, bioinversion between KT stereoisomers appears minimal in calves, studies with individual isomers are needed before any firm conclusions can be drawn about this lack of KT bioinversion.